Filter condenser and brush holder



Nov. 9, 1948.- I K.-.H'. BRAND T 2, FILTER connsnsznrm' anun apmma.

Fiiod lay 16, 1945 INVENTOR- KRISTIAN H. BRANDT ATTORNEY Patented Nov.9, 1948 UNITED STATES PATENT OFFIQE Kristian H. Brandt, Red Bank, N. 1.,signer to the United States of America. as represented by the Secretaryof War Application May 18, 1945, Serial N0. 594,1 Claims. (Cl. 171-324)(Granted under the act of March 8, 1883, is amended April 30, 1928: 3700. G. 757) The invention described herein may be manufactured and usedby or for the Government for governmental purposes, without the paymentto me of any royalty thereon.

This invention relates to fixed capacitors which are especially suitableas filter capacitors tor electrical systems used in vehicles andairplanes. The electrical systems such as ignition systems, generatingand starting equipments, etc., produce considerable interference withthe radio communication equipment also used on these vehicles, unlessthese radio-interference producing systems are provided with theinterference-suppressing filters; the condenser disclosed in thisapplication is particularly suitable for this purpose, and it isincorporated into a brush holder oi a generatonor a motor, thetemperatures of which ordinarily produce a considerable amount ofinterierence.

In order to accomplish proper suppression of the interferencefrequencies produced by the various auxiliary equipment used inconnection with internal combustion engines, it is necessary that thefilter, which, in this case, consists of a shunting condenser, shouldhave sufliciently large capacitance for filtering low frequencies, and aminimum inductance and resistance components in the shunting path of thecondenser, so that the shunting path would provide a very low impedancepath to ground for the interference-producing high frequencies. In thepast, it has been customary to use condensers connected by means ofconducting leads between a line carrying the useful current as well asthe interference signals and ground. When filtering of high frequenciesis required, such arrangement is not satisfactory, since the conductingleads on both sides 01' the condenser, as well as the foil of thecondenser, itself, have sufficient inductance and resistance so as topreclude this shunting path from having sufilciently low shuntingimpedance for high frequencies.

The invention discloses a filtering condenser which is so constructedthat it forms an integral part of a brush holder, the structure of thebrush holder and of the condenser being so arranged that the condenseris closely coupled electrically to the outgoing or incoming circuit orthe machine producing the interference signals. Accordingly, thefiltering condenser has high resonance frequency, since it is nothandicapped by the inductance and resistance components ordinarilyintroduced by the connecting leads; it thus offers a low impedanceshunting pathfor the interference signals. Moreover, the condenser isconstructed to withstand high temperatures, so that it can be mounted inproximity oi the engines and operated over a large temperature range, iscapable oi withstanding vibration, and is not adversely affected bymoisture, oil, grease, or gasoline. i

It is, therefore, an object 01 this invention to provide a combination01' a brush holder and a filter condenser, the condenser beingincorporated into the structure of the brush holder.

It is an additional obiect of this invention to provide a. combinationof a brush holder and a filter condenser, in which the filter condenserhas high resonance frequency, large temperature range, and which isunaffected by vibrations incident to vehicular, aircraft, and othermechanical equipment insta1lations.-

These and other features or the invention will be more easil understooditem the following detailed description and the accompanying drawing, inwhich: f

Figure l is a side view of a brush holder and condenser with the lowerportion of the brush holder sectionalized, in order to illustrate moreclearly the construction of the combination, and Figure 2 is a modifiedstructure of the brush holder and condenser illustrated in Fig. 1.

Referring to Fig. 1, a hollow casing iii made of insulative material,preferably ceramic, acts as a holder for a brush l2, brass insert i3,and a brush spring H which resiliently hold the "crush outwardlyprojecting by being connected to its inner end in any suitable manner.The brush is pro vided with a'. pig tail it which is con cted on oneside to the brush, and on the other do to a brass contact plate i8,which'is held in tight electrical engagement with insert i3 by means oi.a threaded cap ll. Cap i1 consists of an outer, insulative casing i8 andan inner brass insert head 19 which is molded into cap I0, so that thebrass insert head i8 and cap I8 represent an integral structure. Brassinsert head I! is provided with a conical member 20 which engages theconical recess in cap It, so that the latter makes a tight electricalcontact with brass insert i3. and is properly centered by the cone. Pigtail it is soldered to an extension .22 of cap it, with the result thatthere is a low resistance path between pig tail Ill and insert it. Thelatter protrudes beyond the ceramic casing to at 24, and the protrudingportion of the insert is used as a guiding means for the brush, and alsoas a connecting frame between the insert and a terminal brass lug 26which is used for connecting the brush to the outgoing conductor (notindicated in the figare). The lug is soldered to extension so at theinsert by means of a soldering joint to which insures positive contactbetween the lug and the insert. Portions 3t and as oi the inner andouter walls of the ceramic casing iii are provided with metalliccoatings, which may be silver, copper, aluminum, etc., the inner coatingto making positive electrical contact with insert it, while the outercoating 32 is connected by means oi a lead gasket 36 and a set screw illto ground through the outer casing til of the machine. Accordingly, thecondenser is formed by the inner and outer metal coatings on the ceramiccasing iii, the inner coating being connected to the commutator of themachine through brush i2, while the outer coating is grounded by casingto. Euitable dielectric ceramics having proper dielectric constants,proper thermal 'coefilcient or expansion, and capacitance-temperaturecharacteristics may be obtained by using such materials as titaniumoxide, or a mixture of titanium oxide with any of the following oxides:barium oxide, strontium oxide, lead oxide, or calcium oxide. Eitheramorphous or crystalline ceramics may be used, and, in either case, highQ condenser may be obtained by proper blending and processing of theceramic materials, according to well known methods in the art. Positiveelectrical contact between metallic layer'30 and insert it may beimproved by soldering layer 36 to insert 03.

Fig. 2 discloses a modified structure of the brush-holder-condensercombination, the modification residing in the fact that bushing iii hasbeen eliminated completely, and the condenser is formed now between ametallic casing i8 and the outer metallic layer d, which is deposited ona ceramic coating 282, the latter, in turn, being deposited on casingi3. The outer metallic layer 200 is grounded through casing 38 oi themachine, lead gasket 36, and a set screw M, in the manner identical tothat disclosed in fig 1. The advantage of the structure disclosed infig. 2 resides in the fact that it eliminates casing ill and thecapacitance of the condenser now formed between cas-- ing l3, and theouter, metallic layer 200 is larger than the capacitance of thecondenser illustrated in Fig. 1, since the spacing between the condenserplates in Fig. 2 is considerably smaller than the same spacing in Fig.1.

The capacitance of the condenser in Fig. 2 may be increased stillfurther. it so desired, by depositing a plurality of ceramic andmetallic layers in alternate succession in accordance with the methodsdisclosed in my co-pending application for patent titled Capacitance andmethods and apparatus for making the same, Serial Number 547,094, filedJuly 28, 1944. When this is the case, then one series of the metalliclayers is connected to casing l3 and the alternator series of themetallic layers is connected to ground in the manner illustrated in Fig.2.

The advantages of the disclosed condensers are: they may be operatedover a large temperature range; they have high resonance frequencybecause of the inherently low inductance and high C/L ratio, simplicityof construction, ability to resist vibrations, and the use of materialswhich resist moisture, oil, and abrasion-the factors which must bealways considered when filtering condensers for use in connectionwith D.C. or A. C. machines are considered. This is especially the case whensuch machines are a component part of an internal combustion engine.

It is believed that the construction and operation of thebrush-holder-condenser combination ill detail is as well as theadvantages thereof will be apparent from the foregoing description. Itshould be understood that while the invention has been shown in twopreferred iorms reasonable changes and modifications may be made withoutdeparting from the spirit of the invention, as sought to be defined inthe following claims.

I claim:

1. A combination of a brush holder and a filter condenser including ametallic casing, a brush slidably mounted within and protruding throughand fitting said casing, said brush being electrically connected to saidcasing, a dielectric sleeve surrounding the outer surface of saidcasing, and a metallic layer deposited on the outer surface or saiddielectric sleeve and capacitatively adjacent to said casing, wherebysaid metallic casing and said metallic layer form said filter condenser,said layer being adaptable for electrical connection.

2. In an electromagnetic machine, a combination of a brush holder and afilter condenser including a metallic casing, a brush slidably mountedwithin and protruding through and fitting salcl casing, said brush beingelectrically connected to said casing, and said casing extendingoutwardly beyond the outer end of said brush, a dielectric layerdeposited on the outer surface of said casing, and a metallic layercleposited on said dielectric layer, whereby said metallic casing andsaid metallic layer form said filter condenser integrally with saidbrush holder.

3. A combination as defined in claim 2 which further includes a metallicsleeve surrounding said metallic layer, and a direct contact connectionbetween said metallic sleeve and a metallic casing of said machine whileinserted therein.

4. In an electromagnetic machine a combination of a brush holder and afilter condenser including a metallic casing attached to and extendingbeyond the casing of said machine, a helical spring mounted within saidcasing, a brush slidably mounted within and protruding through saidcasing, said helical spring being connected to the inner end portion ofsaid brush, a dielectric layer deposited over the entire outer surfaceoi said casing, and a metallic layer capacitatively adjacent to saidcasing deposited on said dielectric layer, whereby said metallic casingand said metallic layer form said filter condenser said casing and layerbeing adapted for low impedance shunting therethrough.

5. A combination of a brush holder and a filter condenser including ahollow casing made of insulative material, a brush slldably mountedwithin and protruding through said casing, an inner metallic liningwithin said casing electrically connected to said brush, and an outermetallic lining on said casing, said casing and said inner and outerlinings being capacitatively arranged and forming said filter condenser.

6. A combination as defined in claim 5 in which said casing comprises acylindrical ceramic barrel, and said inner and outer linings comprisetwo layers of metal deposited on the inner and outer surfaces of saidbarrel.

'7. A combination as defined in claim 5 in which said casing comprises acylindrical ceramic barrel, said inner and outer linings each comprise alayer of metal baked on the surface of said barrel, and'a metallic bandsurrounding said outer metallic lining for grounding said condenser.

8. A combination of a brush holder and a filter condenser including ahollow ceramic casing having portions of its inner and outer surfacescoatcapacitatively arranged to form said filter condenser.

9. A brush holder of the class described comprising in combination, abrush, a pigtail attached to said brush, a cap of conducting materialelectrically attached to another portion of said pigtail and having agroove formed in its structure, a brush spring resting, against said capand resiliently acting upon said brush in a direction away from saidcap, an inner conducting casing for containing said spring and forengagement with the inner surface of said cap at one end tand having anorifice for the brush to actuate through at the other end, a conductinginsert head coupled to said inner casing and including a member adaptedto fit into said groove and against said cap to make electrical andmechani cal contact therewith, a dielectric element encasing theexternal surface of said inner casing, and a conducting coatin coveringa portion of said element in capacitative alignment with said casing tocomplete a condenser structure, said brush being in series with acapacitative path formed by said condenser to an extraneous source.

10. A brush holder of the class described comprising in combination acommutator brush, a straightened pigtail with one end. portionelectrically attached to said brush, a cap of conducting materialelectrically attached to the opposite end portion of said pigtail andhaving an apexed groove formed in its external surface structure, a coilbrush spring resting against said cap and resiliently acting upon saidbrush in a direction away from said cap and contacting the w,

casing throughout its length, an inner conducting casing for containingsaid spring and 01' engagement at one end with the inner surface of saidcap and having 'an orifice for the brush to actuate therethrough at theother end, a conducting insert head coupled to said casing and having anapexed member fitting into said groove and against said canto makeelectrical andimechanical contact therewith, a dielectric elementREFERENCES; CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,948,417 Fischer Feb. 20, 1934FOREIGN PATENTS Number Country Date 741,971 France Dec. 20, 1932

